Here's a fun little idea I stole from a Convention. Take an image - something large with bulky features is probably better...
Stamp your image on a piece of cardstock just slightly smaller than your card. If you're using a smaller stamp, you can repeat the image multiple times - just do what you can to fill the space.
Then -- cut the image all up! It's going to hurt at first, but trust me, you'll make it. Cut your image into horizontal or vertical strips, arrange them on some matted paper, and glue/tape them down.
Now here are my criticisms of this card:
1) I made the strips too wide -- you're much better off using narrow strips (perhaps 1/2 inch each?) because - believe it or not - it helps make a more solid image. The gaps look less like prison bars...
2) Don't tear your edges -- or, if you have to, wait to do the last side until AFTER you've cut the image into strips. As you can see, mine are a little crooked here, and ultimately the tears don't look all that great. If you wanted, you could always make a green "frame" to go over the top, and tear the edges of the frame's opening instead of actually tearing the stamped image. The choice is yours :)
Either way, this is actually a fun and quick way to make a good looking card. The example I have from the convention is a little different, but you can bet I'll be trying this one a few more times to make sure I get it right!